Turbochargers are widely used on internal combustion engines and, in the past, have been particularly used with large diesel engines, especially for highway trucks and marine applications.
More recently, in addition to use in connection with large diesel engines, turbochargers have become popular for use in connection with smaller, passenger car power plants. The use of a turbocharger in passenger car applications permits selection of a power plant that develops the same amount of horsepower from a smaller, lower mass engine. Using a lower mass engine has the desired effect of decreasing the overall weight of the car, increasing sporty performance, and enhancing fuel economy. Moreover, use of a turbocharger permits more complete combustion of the fuel delivered to the engine, thereby reducing the overall emissions of the engine, which contributes to the highly desirable goal of a cleaner environment.
The design and function of turbochargers are described in detail in the prior art, for example, U.S. Pat. Nos. 4,705,463, 5,399,064, and 6,164,931, the disclosures of which are incorporated herein by reference.
Turbocharger units typically include a turbine operatively connected to the engine exhaust manifold, a compressor operatively connected to the engine air intake manifold, and a shaft connecting the turbine and compressor so that rotation of the turbine wheel causes rotation of the compressor impeller. The turbine is driven to rotate by the exhaust gas flowing in the exhaust manifold. The compressor impeller is driven to rotate by the turbine, and, as it rotates, it increases the air mass flow rate, airflow density and air pressure delivered to the engine cylinders.
As the use of turbochargers finds greater acceptance in passenger car applications, three design criteria have moved to the forefront. First, the market demands that all components of the power plant of either a passenger car or truck, including the turbocharger, must provide reliable operation for a much longer period than was demanded in the past. That is, while it may have been acceptable in the past to require a major engine overhaul after 80,000–100,000 miles for passenger cars, it is now necessary to design engine components for reliable operation in excess of 200,000 miles of operation. It is now necessary to design engine components in trucks for reliable operation in excess of 1,000,000 miles of operation. This means that extra care must be taken to ensure proper fabrication and cooperation of all supporting devices.
The second design criterion that has moved to the forefront is that the power plant must meet or exceed very strict requirements in the area of minimized NOx and particulate matter emissions. Third, with the mass production of turbochargers, it is highly desirable to design a turbocharger that meets the above criteria and is comprised of a minimum number of parts. Further, those parts should be easy to manufacture and easy to assemble, in order to provide a cost effective and reliable turbocharger.
Turbocharger efficiency over a broad range of operating conditions is enhanced if the flow of motive gas to the turbine wheel can be controlled, such as by making the vanes pivotable so as to alter the geometry of the passages therebetween. The design of the mechanism used to effect pivoting of the vanes is critical to prevent binding of the vanes. Other considerations include the cost of manufacture of parts and the labor involved in assembly of such systems.
Prior art mechanisms that attempt to provide reliable mechanisms to this end include U.S. Pat. No. 4,770,603 which discloses an exhaust gas turbocharger comprising a turbine with a guide apparatus including an array of guide vanes arranged concentrically around a rotor axis and pivotable between two end limits and an adjusting mechanism for pivoting the vanes. A first “securing” ring is arranged at the side of a bearing housing for mounting a first trunnion of each guide vane that is also mounted at the side of an oppositely disposed turbine housing. The arrangement makes possible a compact construction that can be fabricated at reduced cost and assembled easily. This is achieved by an assembly containing the guide apparatus and the adjusting mechanism. Further, the assembly includes a second securing ring arranged at the side of a turbine housing for mounting a second trunnion of each guide vane.
However, the above mentioned design of Engels, for example, contains numerous moving parts that must not only be fabricated individually, but that are also costly to assemble, require more maintenance, and have higher failure rates than are desired. In addition, friction wear can be a problem with such a design.
Subsequent efforts in this area have included the approach disclosed in U.S. Pat. No. 6,419,464 (Arnold). The vanes of Arnold are pivoted by two posts extending from opposite surfaces of the vanes. A pivot post is received in a respective hole in one vane surface whereas an actuation post extends from the other side of the vane and is received by a ring. When the ring is pivoted, the actuation post extending from the vane is moved, and, because the pivot post is spatially fixed, the vane is pivoted. In operation under flow conditions, the vanes are under significant forces due to (1) the motive gas, (2) the force applied to pivot the vanes through the actuation post, and (3) the force on the vane about the pivot post. These forces result in a cantilevered load on the vanes which introduce stress in the vanes and the various posts. Over hundreds of thousands of turbocharger cycles, the vanes ultimately become torqued due to the cantilevered loads and hystereis. Over time, the vanes will become begin to deform and stick and ultimately break or lock.
The present inventors thus saw a need for a mechanism to provide a variable geometry turbocharger providing extremely high reliability, being cost efficient and inexpensive to manufacture, and that did not possess the negative qualities of the prior art mechanisms.